The present application relates to a recording apparatus for performing recording on a hologram recording medium on which data is recorded using a moire generated by interference between reference light and signal light and to a recording method for use with the recording apparatus.
For example, as disclosed in each of Japanese Unexamined Patent Application Publication Nos. 2005-250038 and 2007-79438, there is a known hologram recording and reproduction method for performing data recording using a moire generated by interference between signal light and reference light.
In this hologram recording and reproduction method, during recording, signal light that is subjected to space light modulation (for example, light intensity modulation) in accordance with recording data and reference light differing from the signal light are irradiated on a hologram recording medium, a moire generated thereby is formed on the hologram recording medium, and thus data recording is performed.
Furthermore, during reproduction, the reference light is irradiated on the hologram recording medium.
As a result of the reference light being irradiated in this manner, diffraction light in response to a moire formed on a hologram recording medium as described above is obtained. That is, as a result, reproduction light (reproduction signal light) in response to recorded data is obtained. The reproduction light obtained in the manner described above is detected using, for example, an image sensor, such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Oxide Semiconductor) sensor and thus, recorded data is reproduced.
Here, as a hologram recording and reproduction method, similarly to a recording and reproduction technique for an optical disc of the related art, such as, for example, a CD (Compact Disc) or a DVD (Digital Versatile Disc), it is considered that data is recorded along tracks. That is, similarly to the case of an optical disc of the related art, by performing recording/reproduction position control, such as tracking servo control, data recording along tracks is performed.
Furthermore, in the hologram recording and reproduction method, the above-described interference between signal light and reference light causes an image (hologram page) containing information on a plurality of bits to be recorded at this time, recording is performed in such a manner that hologram pages are overlapped (multiplexed), and thus the recording density is increased. That is, regarding the recording material of the hologram recording medium, a monomer is changed to a polymer and thus, recording is performed. Since the density of such a change from a monomer to a polymer is coarse, it is possible to perform multiplexed recording of hologram pages at the same position until the monomer is used up.
FIG. 11 is a conceptual view of such hologram multiplexed recording.
First, in FIG. 11, the solid line indicates a track TR formed on a hologram recording medium. Recording of hologram pages is performed with the track TR being set as the center.
It is assumed in this case that the hologram recording medium has a disc shape, and the track TR is formed in a spiral shape on the hologram recording medium. That is, the track TR in this case is formed in such a manner that a plurality of tracks TR are arranged in the radial direction. Regarding the plurality of tracks TR in the radial direction, in FIG. 11, only three tracks TR1 to TR3 are selected and shown.
As shown in FIG. 11, in hologram multiplexed recording, when recording hologram pages along the tracks TR, each hologram page is recorded in such a manner as to be overlapped in the circumferential direction of the disc.
Furthermore, in hologram multiplexed recording, not only such multiplexing in the circumferential direction of the disc, but also multiplexing in the radial direction is performed. For example, in the case that the amount of recording data is comparatively large and the recording of hologram pages is continuously performed over a plurality of tracks TR, hologram pages recorded between tracks TR are overlapped. Hologram pages adjacent in the radial direction can be recorded in such a manner as to be overlapped as described above, and the interval (track pitch) between tracks TR is set shorter than the radius of the hologram page as shown in the figure. For example, according to the setting of the track pitch in the figure, the recording position in the radial direction of the hologram page on the adjacent track TR2 is a position indicated by the dashed-line circle with the track TR2 being serve as the center.